command/database: add optional position parameter to "searchaddpl"

Closes https://github.com/MusicPlayerDaemon/MPD/issues/1328

src/command/DatabaseCommands.cxx

@@ -199,13 +199,20 @@ handle_searchaddpl(Client &client, Request args, Response &)
 {
 	const char *playlist = args.shift();
 
+	const unsigned position = ParseQueuePosition(args, UINT_MAX);
+
 	SongFilter filter;
 	const auto selection = ParseDatabaseSelection(args, true, filter);
 
 	const Database &db = client.GetDatabaseOrThrow();
 
-	search_add_to_playlist(db, client.GetStorage(),
-			       playlist, selection);
+	if (position == UINT_MAX)
+		search_add_to_playlist(db, client.GetStorage(),
+				       playlist, selection);
+	else
+		SearchInsertIntoPlaylist(db, client.GetStorage(), selection,
+					 playlist, position);
+
 	return CommandResult::OK;
 }
 

src/db/DatabasePlaylist.cxx

@@ -22,6 +22,7 @@
 #include "PlaylistFile.hxx"
 #include "Interface.hxx"
 #include "song/DetachedSong.hxx"
+#include "protocol/Ack.hxx"
 
 #include <functional>
 
@@ -61,3 +62,22 @@ SearchInsertIntoPlaylist(const Database &db, const Storage *storage,
 
 	return n;
 }
+
+void
+SearchInsertIntoPlaylist(const Database &db, const Storage *storage,
+			 const DatabaseSelection &selection,
+			 const char *playlist_name,
+			 unsigned position)
+{
+	PlaylistFileEditor editor{
+		playlist_name,
+		PlaylistFileEditor::LoadMode::TRY,
+	};
+
+	if (position > editor.size())
+		throw ProtocolError{ACK_ERROR_ARG, "Bad position"};
+
+	if (SearchInsertIntoPlaylist(db, storage, selection,
+				     editor, position) > 0)
+		editor.Save();
+}

src/db/DatabasePlaylist.hxx

@@ -42,4 +42,10 @@ SearchInsertIntoPlaylist(const Database &db, const Storage *storage,
 			 PlaylistFileEditor &playlist,
 			 unsigned position);
 
+void
+SearchInsertIntoPlaylist(const Database &db, const Storage *storage,
+			 const DatabaseSelection &selection,
+			 const char *playlist_name,
+			 unsigned position);
+
 #endif